Conventionally, pulse-compression radars are known, which transmit pulse signals, receive reflection waves thereof, and perform a pulse compression on the reflection waves, so as to improve distance resolution and S/N (signal-to-noise ratio). In the case of transmitting the pulse signals having the wide pulse width, since the reflection waves cannot be received while the pulse signals are transmitted, a target object within a close distance cannot be detected. Therefore, pulse signals having a narrow pulse width may be transmitted additionally in order to detect target objects within the close distance. JP2008-527391A and JP5398306B disclose radar apparatuses of such a kind.
The radar apparatus of JP2008-527391A transmits a set of a short pulse signal for close distance, a medium pulse signal for medium distance, and a long pulse signal for far distance. The short pulse signal is a non-modulated pulse and the medium and long pulse signals are modulated pulses.
The radar apparatus of JP5398306B, similar to JP2008-527391A, transmits pulse signals having three kinds of pulse widths. This radar apparatus stores a given number of reception data for each of the three kinds of pulse signals (i.e., for each detectable distance). This radar apparatus performs a pulse integration of the given number of reception data by using FFT (Fast Fourier Transform), DFT (Discrete Fourier Transform), etc., for each of the three kinds of pulse signals. Thus, the S/N can be improved.
However, in the case of transmitting the pulse signals having the three kinds of pulse widths in order as JP2008-527391A and JP5398306B, a transmission time interval between the pulse signals with the same pulse width becomes long. Especially since the pulse signals are transmitted from the radar apparatus at a given angle interval in a bearing direction, space between the pulse signals in the bearing direction becomes wider as they propagate farther from the radar apparatus. Therefore, with the long transmission time interval between the pulse signals for far distance detection, the pulse signals may not meet a target object within a far distance range. In this case, the target object within the far distance range is not detected and/or the S/N does not improve much even by performing the pulse integration.